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External fertilization is a mode of reproduction in which a male organism's sperm fertilizes a female organism's egg outside of the female's body. [1] It is contrasted with internal fertilization , in which sperm are introduced via insemination and then combine with an egg inside the body of a female organism.
Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside in the case of external fertilization. The fertilized egg cell is known as the zygote. [2] [5] To prevent more than one sperm fertilizing the egg , fast block and slow block to polyspermy are used. Fast block, the membrane ...
With external fertilisation, eggs are often laid by the female in a male's territory. [72] [page needed] Male territoriality is particularly common with external fertilisation. Therefore, the male is most closely associated with the embryos. Males may defend their territories and thereby incidentally defend their eggs and young.
In all cases, the eggs are protected until they hatch and the fry become free swimming. Only in some cases does the parent extend protection to mobile juveniles. Among the cichlids and arowanas, extension of brood care to the fry is common, and they have behavioural cues to tell fry swimming and feeding away from the parent that danger is ...
First, external fertilization protects against paternity loss; however, sneaker tactics and strong sperm competition have evolved many times. Second, the earlier release of eggs than sperm gives females an opportunity to flee; however, in many paternal care species, eggs and sperm are released simultaneously.
The other suggests there may someday be a way to prevent serious cases of jaundice in newborns. As women age, the quality of their eggs decreases and they become less useful for in vitro ...
Although biologists' definitions of pregnancy somewhat differ, all members of the family are considered by ichthyologists to display male pregnancy, even those without an external brood pouch. Fertilization may take place in the pouch or in the water before implantation, but in either case, syngnathids' male pregnancy ensures them complete ...
The study, published in Proceedings of the National Academy of Sciences, finds that some dinosaur eggs may have taken six months or more to hatch–much longer than the eggs of dinosaurs' close ...